Accelerating tube with heating means

ABSTRACT

The accelerating tube of the present invention is provided with means for continuously heating the tube while it is in operation. This has the surprising effect of greatly increasing the ability of the tube to withstand high voltages. Thus, an increased operating voltage may be employed when the tube is heated. The heating of the tube drives off condensed gases from the interior surfaces of the tube, while also preventing any condensation of residual gases upon such surfaces. Various means may be provided to heat the tube. It is particularly advantageous to subdivide the tube into tubular sections with separator electrodes or diaphragms therebetween. The ion beam passes within the tube through apertures in the separators. It is preferred to heat the separators by causing electrical currents to pass through the separators. The electrical currents are preferably supplied by a series of generators driven by an insulating shaft. Heat may also be supplied externally to the accelerating tube, by means of heating coils or lamps. Another arrangement is to heat the entire tank in which the tube is enclosed.

United States Patent 72] Inventor Raymond G. Herb Madison, Wk. [21] App]. No. 793,333 [22] Filed Jan. 23, 1969 [45] Patented Dec. 28, 1971 [73] Assignee National Electroetatics Corp.

Mlddleton, Wk.

[54] ACCELERATING TUBE WITH HEATING MEANS 20 Claims, 6 Drawing Figs.

[52] US. Cl 313/15, 313/47, 313/63, 315/539 [51] Int.C1 H01] 7/24, l-l05h 5/02 [50] Field oiSearch .1 313/11,15, 47, 63; 328/233; 315/539, 5.41, 5.42, 5.45, 5.49

[56] References Cited UNITED STATES PATENTS 2,320,685 6/1943 Von Bertele 315/112 2,515,280 7/1950 315/523 2,747,091 5/1956 331/70 2,956,201 10/1960 3l5/5.41 3,449,618 6/1969 Gallagher 313/63 X Primary Examiner-Roy Lake Assistant Examiner-E. R. La Roche AnorneyBurmeister, Palmatier & l-lamby ABSTRACT: The accelerating tube of the present invention is provided with means for continuously heating the tube while it is in operation. This has the surprising effect of greatly increasing the ability of the tube to withstand high voltages. Thus, an increased operating voltage may be employed when the tube is heated. The heating of the tube drives off condensed gases from the interior surfaces of the tube, while also preventing any condensation of residual gases upon such surfaces. Various means may be provided to heat the tube. It is particularly advantageous to subdivide the tube into tubular sections with separator electrodes or diaphragms therebetween. The ion beam passes within the tube through apertures in the separators. It is preferred to heat the separators by causing electrical currents to pass through the separators. The electrical currents are preferably supplied by a series of generators driven by an insulating shaft. Heat may also be supplied externally to the accelerating tube, by means of heating coils or lamps. Another arrangement is to heat the entire tank in which the tube is enclosed.

PATENTED Hinze 19?:

SHEET 2 [IF 3 ACCELERATING TUBE WITII HEATING MEANS This invention relates to accelerating tubes of the general type employed in electrostatic accelerators, in which ions are focused into a beam and are accelerated to a high energy level by an extremely high voltage, applied between the ends of the accelerating tube. In such an accelerator the limiting factor upon the energy to which the ions can be accelerated has generally been found to be the ability of the accelerating tube to withstand the high voltage, without flash-overs or sparking within the tube. A high vacuum is maintained within the tube, but flash-overs may occur due to ionization of the residual gases within the tube. Ordinarily, flash-overs do not occur along the outside of the tube, because the tube is normally surrounded with an insulating atmosphere of a suitable gas or gases at a high pressure. The high-pressure insulating atmosphere affords a greatly increased ability to withstand the high voltages which are impressed between the ends of the accelerating tube.

Because of the desire to accelerate the ions to higher energy levels, efforts have been made to provide accelerating tubes capable of withstanding higher and higher voltages. Such efforts have often involved the provision of longer and longer accelerating tubes, on the theory that the ability of an accelerating tube to withstand a high voltage should be proportional to the length of the tube. However, it has been found that longer accelerating tubes are not capable of withstanding high voltages in proportion to their length. Thus, for example, doubling the length of an accelerating tube does not double the voltage which the tube can withstand. Instead, the maximum permissible voltage is increased by a smaller factor. This relative inefficiency of long accelerating tubes is known as the long tube effect.

One approach to overcoming the long tube effect is disclosed and claimed in the copending application of Raymond G. Herb, Ser. No. 658,002, filed Aug. 2, 1967. In accordance with the invention disclosed and claimed in such copending application, the accelerating tube is divided into a plurality of insulating tubular sections connected end to end, with intermediate electrodes therebetween. The intermediate electrodes include isolating diaphragms which divide the accelerating tube into a plurality of successive chambers. The ion beam passes through apertures in the diaphragms. Evacuating devices, such as ion getter vacuum pumps, are mounted on some or all of the intermediate electrodes and are connected to the isolated chambers for separately evacuating such chambers. The diaphragms, together with the intermediate evacuating devices, greatly increase the ability of the accelerating tube to withstand high voltages. The total permissible voltage becomes substantially proportional to the length of the accelerating tube. The diaphragms, together with the intermediate evacuating devices, prevent any localized sparking or ionization from spreading throughout the entire tube. Thus, the possibility of an overall flash-over is greatly reduced.

The present invention provides another approach to overcoming the long tube effect. In accordance with the present invention, means are provided to heat the accelerating tube to an elevated temperature. This has the surprising effect of greatly increasing the ability of the tube to withstand high voltages. Thus, the maximum permissible voltage becomes virtually proportional to the length of the accelerating tube. The heating of the accelerating tube drives off gases and prevents the subsequent condensation of residual gases upon the internal surfaces of the tube. The gases evolved by the heating of the tube are removed by the vacuum pump or pumps, connected to the tube. Heat is continuously applied to the tube during normal operation. In addition, the tube is preheated to a high temperature before being put into operation.

Various means may be employed to heat the accelerating tube. In one advantageous arrangement, the tube is provided with separators or diaphragms of the type previously discussed. The separators are heated by causing electrical currents to flow through the separators. It is not necessary in all cases to heat every separator. Instead, every second or third separator may be heated. The heat generated in these separators is enough to heat the entire tube to an elevated temperature. The power to heat the separators during normal operation may be provided by a plurality of generators, driven by one or more insulating shafts. Before the high voltage is applied to the tube, the tube may be preheated by causing electrical currents to flow through all or nearly all of the separators. For this purpose, direct connections may be made between the separators and an external power supply. These connections are removed before the high voltage is applied to the tube.

Other means may be employed to heat the accelerating tube. Thus, heating coils or heat lamps may be employed to heat the tube by radiation. 1

Normally, the accelerating tube is enclosed within a tank adapted to hold a high-pressure insulating atmosphere. The tube may be heated by applying heat to the tank, so that the entire tank is heated to an elevated temperature.

The heating of the accelerating tube eliminates or minimizes the evolution of gases by any localized sparking or other discharge which may occur in the tube. The evolution of gases tends to spread any such discharge throughout the tube so as to cause a major flash-over. Thus, the heating of the tube minimizes the chance of a flash-over. Considerably higher voltages can be applied to the heated tube than could otherwise be employed.

To minimize the loss of heat, insulating material may be provided around the tank in which the accelerating tube is enclosed. The entire tank may be heated by providing heating coils between the insulating material and the tank.

Various other objects, advantages and features of the present invention will appear from the following description, taken with the accompanying drawings, in which;

FIG. I is a fragmentary longitudinal section taken through an accelerating tube to be described as an illustrative embodiment of the present invention.

FIG. 2 is a longitudinal section, taken through a high-voltage accelerator which incorporates the accelerating tube of FIG. 1.

FIGS. 3, 4, 5 and 6 are fragmentary longitudinal sections, similar to a portion of FIG. 2, but showing four modified means for heating the accelerating tube.

It will be seen that FIGS. 1 and 2 of the drawings illustrate an electrostatic accelerator 10 which utilizes an accelerating tube 12. A high-voltage electrostatic generator 14 is employed to provide the operating voltage for the accelerating tube 12. Preferably, the accelerating tube 12 and the high-voltage generator 14 are enclosed within a tank 16 which may be made of steel or the like. The tank 16 is adapted to hold an insulating atmosphere which surrounds the accelerating tube 12 and the high-voltage generator 14, so that the generator can develop and maintain a higher voltage than would otherwise be possible. The insulating atmosphere normally comprises a gas of high dielectric strength, such as sulfur hexafluoride, for example, which is compressed to a high pressure.

The illustrated high-voltage generator 14 comprises a highvoltage electrode 18 on which electrostatic charges are accumulated to provide the high operating voltage for the accelerating tube 12. The high-voltage electrode I8 is centrally disposed in one end portion of the tank 16 and is supported by a plurality of elongated insulators 20, connected between the electrode 18 and a grounded support 22 at the opposite end of the tank 16. The illustrated insulators 20 are in the form of sectionalized pillars or columns. Thus, each insulator 20 isdivided into a plurality of major sections 23. To assist in producing an even potential gradient along the insulators 20, it is preferred to provide ring-shaped electrodes 24 between the sections 23 of the insulators.

Each section 23 of each insulator 20 is preferably subdivided into a plurality of insulating laminations 26 with conductive layers of plates 28 therebetween. Potential distribution rings 30 are preferably mounted on the plates 28.

The insulating laminations 26 of the insulators are preferably made ofa suitable ceramic material. The insulating laminations 26 are suitably bonded to the metal rings 24 and plates 28. it is preferred to employ the metallic bonding method disclosed and claimed in the copending application of Raymond G. Herb, Ser. No. 557,787, filed June 15, I966. However, other suitable bonding methods may be employed, including bonding methods utilizing nonmetallic bonding adhesives. lt will be understood that the construction of the insulators 20 is not involved in the present invention and that any suitable construction may be employed.

The high-voltage electrostatic generator 14 comprises a conveyor 32 whereby electrostatic charges are carried to the high-voltage electrode 18. Electrostatic charges may also be carried from the high-voltage electrode 18 to the grounded support 22 and thence to the tank 16. The illustrated conveyor 32 comprises an endless charge-carrying member 34, trained around two pulleys 36 and 38. The pulley 36 is adjacent the grounded support 22 and is connected thereto electrically, while the pulley 38 is mounted within and connected to the high-voltage electrode 18. Any suitable motor may be employed to drive the pulley 36.

The endless charge-carrying member 34 is preferably in the form of one or more pellet trains, as disclosed and claimed in the copending application of Raymond G. Herb and James A. Ferry, Ser. No. 557,818, filed June 15, [966. However, the charge-carrying member 34 may assume various forms, such as the conventional belt conveyor.

Electrostatic charges are produced on the endless member 34 as it leaves the pulley 36. These charges are carried to the pulley 38 and thence to the high-voltage electrode 18. Any suitable system may be employed for charging the endless member 34. As shown, a charging electrode 40 is disposed opposite the endless member 34 as it leaves the pulley 36. A power supply 42 is employed to produce a high direct voltage on the electrode 40 relative to ground. The high voltage on the electrode 40 induces charges on the endless member 34 as it leaves the pulley 36.

As illustrated, the accelerating tube 12 extends from the high-voltage electrode 18 to the grounded support 22, and then through the grounded support to an external target area. Thus, the entire voltage developed on the electrode 18 is impressed between the ends of the accelerating tube 12. This voltage is employed to accelerate a beam of ions to high energy levels. The ions are produced by an ion source 44, mounted on the end of the accelerating tube within the high-voltage electrode 18. The ions may comprise protons, deuterons, or various other charged particles.

As shown to best advantage in FIG. 1, the accelerating tube 12 comprises an elongated cylindrical wall 46 made principally of an insulating material, such as a suitable ceramic. The ion beam 48 is directed along the axis of the tube 12.

Preferably, the cylindrical wall 46 is divided into a plurality of principal sections 50, with potential distributing rings or flanges 52 therebetween. The flanges 52 are preferably made of metal, suitably bonded to the ends of the insulating sections As shown, the insulating sections are further subdivided into ring-shaped insulating laminations 54, with conductive plates 56 therebetween. The provision of the plates 56 is of assistance in achieving an even distribution of the potential along the accelerating tube 12. The ceramic laminations 54 are suitably mounted to the metal plates. It is preferred to utilize the metallic bonding method disclosed and claimed in the previously mentioned Herb application Ser. No. 557,787, filed June 15, l966, but other suitable bonding methods may be employed, including methods which utilize a nonmetallic bonding agent. Either metallic or nonmetallic bonding methods may be employed to bond the flanges 52 to the ends of the cylindrical sections 50.

The flanges or rings 52 constitute intermediate electrodes which are effective in maintaining a substantially uniform potential gradient along the length of the accelerating tube 12.

As shown in FIG. 1, every second flange 52 is connected to one of the potential distributing rings 24 which are mounted on the insulators 20.

The long tube effect has been encountered with accelerating tubes of the construction thus far described. Thus, the entire tube will not withstand as great a potential gradient as will the individual sections, when employed separately. As a step toward overcoming this difficulty, the accelerating tube 12 is divided into relatively isolated sections by providing separators or isolating diaphragms 58 across the inside of the tube at regular intervals. The ion beam 48 passes through an axial aperture 60 in each of the separators 59. As shown, each separator 58 is in the form of a plate supported by one of the ring-shaped flanges or electrodes 52.

The separators 58 tend to inhibit the spread of any localized discharge throughout the length of the accelerating tube 12. However, it has been found that the separators 58 are not entirely effective in this regard.

In accordance with the present invention, means are provided to heat the accelerating tube to an elevated temperature. This has been found to be highly effective in overcoming the long tube effect. Thus, the entire tube will withstand a potential gradient substantially as great as can be withstood by the individual sections. It is believed that the heating of the tube drives off condensed gases therefrom and prevents any residual gases from subsequently condensing upon the interior surfaces of the tube 12. Thus, minor localized discharges do not cause the evolution of any substantial quantities of gases. With prior accelerating tubes, the condensed gases were copiously evolved by any minor discharge, and the evolved gases were effective to spread the discharge throughout the accelerating tube, so as to cause major flash-overs. Such flashovers may be so destructive as to put the accelerating tube out of service.

It is particularly advantageous to heat the tube by applying heat to the separators, from which the heat is conducted and radiated to the other components of the tube. While all of the separators 58 can be heated directly, it is normally sufficient to heat every second or third separator. In that case, the intermediate separators are indirectly heated by radiation and conduction. While the heating of the separators is especially important in overcoming the long tube effect, the heating of the walls and the other portions of the accelerating tube is also highly beneficial, because the condensation of residual gases on the walls is thereby prevented or greatly reduced.

Various means may be employed to supply heat to some or all of the separators 58. As shown in FIG. 1, some of the separators 58 are heated by causing electrical currents to pass along the separators. The illustrated separators are in the form of metal plates which extend diametrically across the inside of the accelerating tube 12. Two terminals 62 and 64 are connected to widely spaced points on the separator plates 58. As shown, the terminals 62 and 64 are connected to diametrically opposite points on the circular separator plates 58. The terminals 62 and 64 preferably extend out of the accelerating tube 12 to feed through insulators 66 and 68, mounted in the flanges 52. The separator plates 58 are supported by the terminals 62 and 64.

Suitable means are provided to supply electrical currents to the terminals 62 and 64. As shown, the electrical power is supplied by a generator 70 and a transformer 72. The generator 70 produces a alternating voltage which is impressed across the primary winding 74 of the transformer 72. The secondary winding 76 of the transformer 72 is connected between the terminals 62 and 64.

As shown in FIGS. 1 and 2, every other separator 58 is supplied with a heating current. The other separators are heated indirectly by radiation.

Due to the high potential gradient along the accelerating tube 12, each separator 58 is at a different voltage. This complicates the supply of electrical power to the separators. To overcome this complication a separate generator 70 is employed for each of the directly heated separators 58. Each generator is mounted on the intermediate electrode or ring 24 corresponding to the particular separator 58. All of the generators 70 are arranged coaxially with insulating shafts 78 therebetween. A single motor 80 is employed to drive all the generators 70. The motor 80 is coupled to the lowermost generator 70 and is mounted adjacent the grounded support 22. One of the generators 70 is preferably provided within the high-voltage electrode 18. This generator may be employed to energize the ion source 44.

One or more vacuum pumps 81 are preferably connnected to the accelerating tube 12. The pumps 81 are preferably of the ion getter type. The gases evolved by the heating of the accelerating tube 12 are absorbed or otherwise removed by the vacuum pumps 81. As shown, one vacuum pump 81 is connected to the lower end of the tube 12, near the grounded base 22. Another vacuum pump 81 is mounted within the high-voltage electrode 18 and is connnected to the upper end of the tube 12. The power to operate this pump 81 may be derived from the generator 70 within the high-voltage electrode 18.

It is preferred to preheat the accelerating tube 12 to an elevated temperature for a considerable period of time before the high voltage is applied to the tube. The heating of the tube drives off gases which are absorbed by the vacuum pumps 81. For preheating purposes, all of the separators 58 may readily be heated by connecting leads directly to the terminals 62 and 64 of the various separators. The leads may be connected to an external power supply, outside the tank 16. When the preheating cycle has been completed, these leads may be disconnected from the accelerating tube so that the high voltage can be applied.

During normal operation, the generators 70 provide power to heat some of the separators 58 continuously. While enough generators could be provided to heat all of the separators, it is generally sufficient to heat every second or third separator. The intermediate separators are heated by radiation and conduction. This is also true of the walls andzother components of the accelerating tube 12, so that the entire tube is maintained at an elevated temperature, sufficient to prevent any substantial condensation of the residual gases on the interior surfaces of the tube.

FIGS. 3, 4 and 5 show alternative arrangements for heating the accelerating tube 12. These arrangements obviate the complications involved in supplying electrical heating currents t0 the individual separators 58. As shown in FIG. 3, a heating coil 82 is provided near the grounded end of the accelerating tube 12. The heating coil 82 may be of the Calrod type or any other suitable type. Radiant heat is supplied to the accelerating tube 12 by the heating coil 82. Electrical leads 84 and 86 are connected to the heating coil 82 and are brought out of the tank 16 by means of feedthrough insulators 88 and 90. Thus, the heating coil may be energized from a conventional power line 92. A switch 94 is preferably connected between one of the leads and the power line 92.

In the arrangement of FIG. 4, the heating coil 82 is replaced with a heating lamp 96 which supplies radiant heat to the accelerating tube 12. FIG. 4 also illustrates another heating arrangement, utilizing an elongated heating coil 98 extending longitudinally along the inner cylindrical wall of the tank 16. The heating coil 98 may extend along the entire length of the accelerating tube, or any desired portion thereof. Here again, leads 100 and 102 are brought out of the tank 16 from the coil 98 by means of feedthrough insulators 104 and 106. A switch 108 is connected into the lead 100. It will be understood that the leads 100 and 102 may be connected to a conventional power line.

The various external heating devices 82, 96 and 98 tend to heat the tank I6 to a considerable extent as well as the accelerating tube 12. This is particularly true of the elongated heating coil 98, which is adjacent the cylindrical wall of the tank. T0 conserve heat, while preventing the overheating of the space around the tank 16, it is preferred to provide a jacket of insulation 110 around the outside of the tank 16. This insulating jacket may be employed to advantage in the embodiment of FIGS. 1 and 2, as well as in the embodiments ofFIGS. 3 and 4.

FIG. 5 illustrates another modified arrangement in which the entire tank 16 is heated by suitable heating coils I 12 or the like. As shown, the heating coils 112 are located between the outside of the tank 16 and the insulatingjacket 110. The heat supplied to the tank 16 is transferred to the accelerating tube 12 by radiation and conduction, so that the entire accelerating tube is heated to an elevated temperature. The heating of the tube is highly beneficial in overcoming the long tube effect, so that the entire tube will withstand voltage gradients corresponding to the gradients that can be withstood by the individual sections. The heating of the accelerating tube drives off condensed gases from all portions of the tube, and prevents the subsequent condensation of residual gases. Thus, there is no substantial quantity of condensed gases to be evolved by any slight discharge of a localized character. Accordingly, localized discharges will remain localized and will not be propagated throughout the accelerating tube.

Even if the separators 58 are not provided, the heating of the accelerating tube 12 is beneficial to a considerable extent in minimizing the long tube effect, so that the ability of the accelerating tube to withstand high voltages is increased. Accelerating tubes of many different constructions can benefit considerably from the heating of the tube to prevent the con densation of residual gases within the tube.

The temperature to which the accelerating tube is heated is not critical and can be widely varied. In an accelerating tube utilizing electrically heated separators, the temperature of the separators has been maintained at about 250 C. with highly successful results. Higher or lower temperatures can be employed under various circumstances.

The heating of the accelerating tube makes it possible to utilize a greatly increased operating voltage between the ends of the tube. In this way, the ions can be accelerated to much higher energy levels. All of this is accomplished without increasing the length of the accelerating tube. For any particular maximum operating voltage, the heating of the accelerating tube makes it possible to employ a shorter accelerating tube and a more compact machine generally.

It will be understood that external heating of the accelerating tube and electrical heating of the separators may be employed either simultaneously or separately. The external heating may be produced by any suitable heating element. When electrical heating of the separators is employed, one of the leads connected to each separator may be connected to the corresponding flange, while the other is brought out of the accelerating tube by a feedthrough insulator. In some cases, the generators can be employed without the stepdown transformers. Various insulating drives can be employed between the successive generators.

FIG. 6 illustrates another modified arrangement for heating the accelerating tube 12. In this arrangement, the tube 12 is heated by a plurality of external heating elements 114, mounted close to the tube 12 at various stations along the length of the tube. The use of the external heating elements 114 is an alternative to electrically heating the diaphragms or separator plates 58. Inasmuch as the heating elements 114 are at different potentials, the heating elements are preferably energized by the generators 70. As shown, each heating element 114 is opposite one of the electrode rings 52 on the accelerating tube 12. The heating elements 114 may be in the form of heating coils, heat lamps or the like. While all of the rings 52 could be provided with heating elements, it is generally sufficient to provide one heating element for every second or third ring. During normal operation, the heating elements 114 are preferably energized continuously.

Various other modifications, alternative constructions and equivalents may be employed, as will be understood by those skilled in the art.

Iclaim:

]. In a high-voltage accelerator,

the combination comprising an elongated electrically insulating accelerating tube,

source means connected to one end of said tube for directing a beam of charged particles, along said tube,

means for producing a high voltage between said source means and the opposite end of said tube to accelerate the charged particles,

heating means for heating said tube to an elevated temperature to enhance the ability of said tube to withstand high voltages,

and means for insulating said heating means from said high voltage.

2. The combination of claim 1, in which said heating means include electrically conductive separators in said tube,

and means for passing electrical currents along said separators to produce electrical heating thereof,

said tube having electrically insulating sections interspersed between said separators.

3. The combination of claim 1,

in which said heating means include a heating coil for heating said tube by radiant heat.

4. The combination of claim 1,

in which said heating means include a heat lamp for heating said tube by radiant heat.

5. The combination of claim 1,

in which said heating means include a heating element spaced from said tube to produce heating thereof.

6. The combination of claim 5,

including heat insulation disposed around said tube and said heating element to minimize the loss of heat therefrom.

7. The combination of claim 1,

including a tank surrounding said tube and spaced outwardly therefrom,

said heating means comprising a heating element between said tank and said tube.

8. The combination of claim 7,

including heat insulation around said tank to conserve the heat generated by said heating element.

9. The combination of claim 1,

including a tank surrounding said tube and spaced outwardly therefrom,

said heating means comprising means for heating said tank.

10. The combination of claim 9,

including heat insulation around said tank and said heating means to reduce heat loss therefrom.

11. The combination of claim 1,

including a plurality of apertured separators extending across said tube and spaced therealong,

said tube having electrically insulating sections interspersed between said separators.

12. In a high-voltage accelerator,

the combination comprising an accelerating tube having a plurality of tubular electrically insulating sections joined together end to end,

a plurality of separators disposed between the successive sections to isolate the sections,

a particle source connected to one end of said accelerating tube for directing a beam of charged particles along said accelerating tube,

said separators having aligned openings therein to provide for the passage of the beam,

means for producing a high voltage between the source and the opposite end of said tube for accelerating the charged particles,

heating means for heating at least some of said separators to enhance the ability of said accelerating tube to withstand high voltages,

and means for insulating said heating means from said high voltage.

13. The combination of claim l2,

in which said separators comprise metal plates disposed between said sections.

14. The combination of claim 12,

in which said separators comprise electrically conductive members, 1

said heating means comprising means for causing electrical currents to flow along said electrically conductive members to produce electrical heating thereof.

15. The combination of claim 12,

in which said separators comprise metal plates disposed between said sections,

said heating means comprising means for causing electrical currents to flow along said plates to produce electrical heating thereof.

16. The combination of claim 12,

in which each separator comprises a conductive member extending across the inside of said tube between the adjacent sections,

an annular mounting flange disposed between said adjacent sections,

a pair of conductive leads extending outwardly from said conductive member to support said conductive member on said mounting flange,

and at least one feedthrough insulator to carry one of said leads outwardly through said mounting flange,

said heating means comprising means for causing an electrical current to flow through said leads and said conductive member to produce electrical heating thereof.

17. The combination of claim 12,

in which said separators comprise conductive members disposed between said sections,

said heating means comprising a plurality of electrical generators for causing currents to flow along said conductive members to produce electrical heating thereof,

and insulating drive means extending between said generators and along said tube for driving said generators.

is. The combination of claim 17,

including transformers connected between said generators and said conductive members.

19. The combination of claim 1,

in which said heating means comprise heating elements adjacent said tube at spaced points therealong.

20. The combination of claim 19,

including a plurality of electrical generators for energizing said heating elements,

and insulating drive means extending between said generators and along said tube for driving said generators. 

1. In a high-voltage accelerator, the combination comprising an elongated electrically insulating accelerating tube, source means connected to one end of said tube for directing a beam of charged particles, along said tube, means for producing a high voltage between said source means and the opposite end of said tube to accelerate the charged particles, heating means for heating said tube to an elevated temperature to enhance the ability of said tube to withstand high voltages, and means for insulating said heating means from said high voltage.
 2. The combination of claim 1, in which said heating means include electrically conductive separators in said tube, and means for passing electrical currents along said separators to produce electrical heating thereof, said tube having electrically insulating sections interspersed between said separators.
 3. The combination of claim 1, in which said heating Means include a heating coil for heating said tube by radiant heat.
 4. The combination of claim 1, in which said heating means include a heat lamp for heating said tube by radiant heat.
 5. The combination of claim 1, in which said heating means include a heating element spaced from said tube to produce heating thereof.
 6. The combination of claim 5, including heat insulation disposed around said tube and said heating element to minimize the loss of heat therefrom.
 7. The combination of claim 1, including a tank surrounding said tube and spaced outwardly therefrom, said heating means comprising a heating element between said tank and said tube.
 8. The combination of claim 7, including heat insulation around said tank to conserve the heat generated by said heating element.
 9. The combination of claim 1, including a tank surrounding said tube and spaced outwardly therefrom, said heating means comprising means for heating said tank.
 10. The combination of claim 9, including heat insulation around said tank and said heating means to reduce heat loss therefrom.
 11. The combination of claim 1, including a plurality of apertured separators extending across said tube and spaced therealong, said tube having electrically insulating sections interspersed between said separators.
 12. In a high-voltage accelerator, the combination comprising an accelerating tube having a plurality of tubular electrically insulating sections joined together end to end, a plurality of separators disposed between the successive sections to isolate the sections, a particle source connected to one end of said accelerating tube for directing a beam of charged particles along said accelerating tube, said separators having aligned openings therein to provide for the passage of the beam, means for producing a high voltage between the source and the opposite end of said tube for accelerating the charged particles, heating means for heating at least some of said separators to enhance the ability of said accelerating tube to withstand high voltages, and means for insulating said heating means from said high voltage.
 13. The combination of claim 12, in which said separators comprise metal plates disposed between said sections.
 14. The combination of claim 12, in which said separators comprise electrically conductive members, said heating means comprising means for causing electrical currents to flow along said electrically conductive members to produce electrical heating thereof.
 15. The combination of claim 12, in which said separators comprise metal plates disposed between said sections, said heating means comprising means for causing electrical currents to flow along said plates to produce electrical heating thereof.
 16. The combination of claim 12, in which each separator comprises a conductive member extending across the inside of said tube between the adjacent sections, an annular mounting flange disposed between said adjacent sections, a pair of conductive leads extending outwardly from said conductive member to support said conductive member on said mounting flange, and at least one feedthrough insulator to carry one of said leads outwardly through said mounting flange, said heating means comprising means for causing an electrical current to flow through said leads and said conductive member to produce electrical heating thereof.
 17. The combination of claim 12, in which said separators comprise conductive members disposed between said sections, said heating means comprising a plurality of electrical generators for causing currents to flow along said conductive members to produce electrical heating thereof, and insulating drive means extending between said generators and along said tube for driving said generators.
 18. The combination of claim 17, including transformers connected between said generatorS and said conductive members.
 19. The combination of claim 1, in which said heating means comprise heating elements adjacent said tube at spaced points therealong.
 20. The combination of claim 19, including a plurality of electrical generators for energizing said heating elements, and insulating drive means extending between said generators and along said tube for driving said generators. 